Hot, Humid, but Cooler Days Possible around the 4th of July

The humidity returned Thursday courtesy of a warm front that moved through and stalled to the north and east of Southern Illinois. Thoughout  Friday, a lot of cloud cover and pop up showers and storms kept temperatures down, the humidity was somewhat oppressive with dewpoints around 70˚.

Friday afternoon, as a weak shortwave trough traversed north/northeast from Northwest Missouri to Central Wisconsin, it provided enough upper level lift to fuel showers and storms that will diminish as the wave gets further away and the heating of the day is lost.

Shortwave trough is circled. Responsible for Friday's storm activity

A larger trough will track north and west of the area through Saturday and fire storms across the eastern Plains into the Upper Midwest and result in more popup variety showers and storms locally Saturday afternoon. As the line of strong storms progresses east Saturday evening, it will lose intensity and may move into Southern Illinois. Storms will not be severe when they arrive into Southern Illinois.

Larger trough is shown with a brown dashed line as it circulates around parent low near Canadian border.

Behind the trough that brushes by on Sunday morning, eventually a weak ridge will set up over the Southern half of the U.S. which should limit moisture and ultimately storm chances for Monday. It doesn't last long as a climatologically stronger cold front approaches from the northwest late Monday. At this time, it appears possible showers and storms may arrive into some of our northern counties (near I-64) late Monday night. As the front slowly drops south and bisects Southern Illinois, more showers and storms will be expected Tuesday.

GFS Precipitation map late Tuesday. Cold front is easily visible close to the Ohio River.

Behind the cold front, high pressure will move in and bring dry and cooler weather with temperatures likely running 5-10˚ below normal through Thursday (July 3rd). At this point, the 4th of July looks to be mainly dry outside a chance for an isolated shower or storm as the upper level flow begins to transition back as a ridge builds over the Plains.

We're in that time of the year where the atmosphere moves slowly over the Middle Mississippi Valley and major weather features are typically more associated with the jetstream which has spent most of the summer thus far in the far northern U.S. Without decent winds aloft, much of the storms we see this time of year are of the popup variety.